Amazon ads are already distinguished from AdSense ads because the two look so completely different.

As long as ads from your other networks don't look like AdSense, I don't believe there is any potential problem.

If some of your other ads look too much like AdSense, I think the AdSense policies provide a few examples of approved text that you can place, for example, above your AdSense ads. "Ads by Google" might have been one of the approved snippets, but my recollection might be out of date, so do check the policies first yourself before doing anything.

Don't identify your AdSense ads with any text not specifically suggested by Google, because they also have a policy about ways you must not identify AdSense ads.